U.S. patent number 6,783,446 [Application Number 09/256,707] was granted by the patent office on 2004-08-31 for chemical mechanical polishing apparatus and method of chemical mechanical polishing.
This patent grant is currently assigned to NEC Electronics Corporation. Invention is credited to Mieko Suzuki, Yasuaki Tsuchiya.
United States Patent |
6,783,446 |
Suzuki , et al. |
August 31, 2004 |
**Please see images for:
( Certificate of Correction ) ** |
Chemical mechanical polishing apparatus and method of chemical
mechanical polishing
Abstract
There is provided an apparatus for polishing a substrate,
including (a) a polishing pad formed with a plurality of
through-holes through which polishing material is supplied to a
surface of the polishing pad, (b) a level block on which the
polishing pad is mounted, and (c) a rotatable carrier for
supporting a substrate thereon, the carrier being positioned in
facing relation with the level block, the level block being
rotatable around a rotation axis thereof with the rotation axis
being moved along an arcuate path, and causing the polishing pad to
make contact with the substrate for polishing the substrate, the
polishing pad having a first ring-shaped region concentric thereto
where no through-holes are formed. For instance, the first
ring-shaped region has a width greater than 10%, but smaller than
95% of a radius of the polishing pad. The apparatus enhances
uniformity in polishing a substrate.
Inventors: |
Suzuki; Mieko (Tokyo,
JP), Tsuchiya; Yasuaki (Tokyo, JP) |
Assignee: |
NEC Electronics Corporation
(JP)
|
Family
ID: |
12717448 |
Appl.
No.: |
09/256,707 |
Filed: |
February 24, 1999 |
Foreign Application Priority Data
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Feb 26, 1998 [JP] |
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10-045372 |
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Current U.S.
Class: |
451/288; 451/261;
451/41; 451/283 |
Current CPC
Class: |
B24B
37/26 (20130101); B24B 57/02 (20130101); B24B
37/04 (20130101) |
Current International
Class: |
B24B
37/04 (20060101); B24B 57/02 (20060101); B24D
13/00 (20060101); B24D 13/14 (20060101); B24B
57/00 (20060101); B24B 029/00 () |
Field of
Search: |
;451/41,268,283,287,288,60,271,291 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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513389 |
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Jan 1993 |
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JP |
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301772 |
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Apr 1997 |
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TW |
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Primary Examiner: Hail, III; Joseph J.
Assistant Examiner: Grant; Alvin J
Attorney, Agent or Firm: Hayes Soloway P.C.
Claims
What is claimed is:
1. An apparatus for polishing a substrate, comprising: (a) a
polishing pad formed with a plurality of through-holes through
which polishing material is supplied to a surface of said pad; (b)
a level block on which said polishing pad is mounted; and (c) a
rotatable carrier for supporting a substrate thereon, said carrier
being positioned in facing relation with said level block; said
level block being rotatable around a rotation axis thereof with
said rotation axis being moved along an arcuate path, and causing
said polishing pad to make contact with said substrate for
polishing said substrate, said polishing pad having a first
ring-shaped region concentric thereto where no through-holes
through which polishing material is supplied are formed.
2. The apparatus as set forth in claim 1, wherein said first
ring-shaped region has a width equal to or greater than 10% of a
radius of said polishing pad.
3. The apparatus as set forth in claim 2, wherein said first
ring-shaped region has a width equal to or greater than 20% of a
radius of said polishing pad.
4. The apparatus as set forth in claim 1, wherein said
through-holes are positioned in alignment with a peripheral region
of said substrate when an axis of said level block is in alignment
with an axis of said carrier.
5. The apparatus as set forth in claim 1, wherein said
through-holes are positioned in a second ring-shaped region having
an outer periphery common to an outer periphery of said polishing
pad and having a width equal to 5% or smaller of a radius of said
polishing pad.
6. The apparatus as set forth in claim 1, wherein said polishing
pad includes a circular region concentric to said polishing pad and
located inside said first ring-shaped region, and a third
ring-shaped region located outside said first ring-shaped region,
said circular region and said third ring-shaped region including
said through-holes therein.
7. The apparatus as set forth in claim 6, wherein said third
ring-shaped region has an outer periphery common to an outer
periphery of said polishing pad.
8. The apparatus as set forth in claim 6, wherein said
through-holes formed in said third ring-shaped region are
positioned in alignment with a peripheral region of said substrate
when an axis of said level block is in alignment with an axis of
said carrier.
9. The apparatus as set forth in claim 1, wherein a total area of
said through-holes varies in a radius-wise direction of said
polishing pad.
10. The apparatus as set forth in claim 9, wherein the number of
said through-holes per a unit area decreases in a direction from an
outer periphery to a center of said polishing pad.
11. The apparatus as set forth in claim 9, wherein diameters of
said through-holes decrease in a direction from an outer periphery
to a center of said polishing pad.
12. An apparatus for polishing a substrate, comprising: (a) a
polishing pad formed with a plurality of through-holes through
which polishing material is supplied to a surface of said polishing
pad; (b) a level block on which said polishing pad is mounted; and
(c) a rotatable carrier for supporting a substrate thereon, said
carrier being positioned in facing relation with said level block;
said level block being rotatable around a rotation axis thereof
with said rotation axis being moved along an arcuate path, and
causing said polishing pad to make contact with said substrate for
polishing said substrate, said polishing pad having a circular
region concentric thereto where no through-holes through which
polishing material is supplied are formed.
13. The apparatus as set forth in claim 12, wherein said circular
region has a radius equal to or smaller than 95% of a radius of
said polishing pad.
14. The apparatus as set forth in claim 12, wherein said circular
region has a radius equal to or greater than 30% of a radius of
said polishing pad.
15. The apparatus as set forth in claim 12, wherein said
through-holes are positioned in alignment with a peripheral region
of said substrate when an axis of said level block is in alignment
with an axis of said carrier.
16. The apparatus as set forth in claim 12, wherein said
through-holes are positioned in a ring-shaped region having an
outer periphery common to an outer periphery of said polishing pad
and having a width equal to 5% or smaller of a radius of said
polishing pad.
17. The apparatus as set forth in claim 12, wherein a total area of
said through-holes varies in a radius-wise direction of said
polishing pad.
18. The apparatus as set forth in claim 17, wherein the number of
said through-holes per a unit area decreases in a direction from an
outer periphery to a center of said polishing pad.
19. The apparatus as set forth in claim 17, wherein diameters of
said through-holes decrease in a direction from an outer periphery
to a center of said polishing pad.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus for polishing a substrate for
planarization by chemical mechanical polishing. The invention
relates further to a method of chemical mechanical polishing.
2. Description of the Related Art
FIGS. 1A to 1E illustrate respective steps in a method of forming a
buried metal layer in a semiconductor device.
First, as illustrated in FIG. 1A, a semiconductor substrate 101
including active devices fabricated thereon is covered entirely
with an insulating film 102.
Then, a resist film 105 having a certain pattern is formed on the
insulating film 102, and subsequently, the insulating film 102 is
etched with the patterned resist film 105 being used as a mask, to
thereby form a contact hole 106 through the insulating film 102, as
illustrated in FIG. 1B.
After removal of the resist film 105, as illustrated in FIG. 1C, a
barrier film 103 composed of metal such as Ti or Ta is deposited
over the insulating film 102 so that the contact hole 106 is
covered at a sidewall and a bottom thereof with the barrier film
103.
Then, as illustrated in FIG. 1D, an electrically conductive layer
104 is deposited over the product to thereby fill the contact hole
106 with the electrically conductive layer 104.
Then, the electrically conductive film 104 is planarized by means
of a chemical mechanical polishing apparatus 107, as illustrated in
FIG. 1E. Thus, a buried metal layer 108 is formed.
The chemical mechanical polishing apparatus 107 includes a carrier
on which a wafer to be polished is fixed, and a rotatable level
block on which a polishing pad is mounted. A wafer is compressed
onto a rotating polishing pad to thereby be polished. While a wafer
is being polished by the polishing pad, polishing powder such as
alumina or silica, and polishing slurry containing etchant such as
H.sub.2 O.sub.2 are supplied between the polishing pad and the
wafer.
FIG. 2 illustrates a conventional apparatus for polishing a wafer
by chemical mechanical polishing. The illustrated apparatus is
comprised of a level block 23 connected to a rotatable shaft 24, a
polishing pad 29 fixed onto the level block 23, a wafer holder 26
connected to a rotatable shaft 27 and holding a wafer 25 on a
bottom thereof, and a slurry source 30 supplying polishing slurry
onto the polishing pad 29 through a slurry supply port 21.
The wafer 25 is sandwiched between the polishing pad 29 and the
wafer holder 26. While the wafer 25 is being polished by the
polishing pad 29, polishing slurry 22 is supplied between the
polishing pad 29 and the wafer 25 around a periphery of the wafer
25.
Though the illustrated apparatus is designed to have one wafer
holder 26, the apparatus may be designed to have a plurality of
wafer holders 26. For instance, the apparatus may be designed to
have four wafer holders 26 equally spaced from one another above
the level block 23 in order to concurrently polish four wafers at a
time.
A conventional apparatus for polishing a wafer, such as the
apparatus illustrated in FIG. 2, is accompanied with a problem of
non-uniformity in polishing speed in a wafer, which results in that
a wafer is polished around a center thereof to a greater degree
than a periphery thereof.
In order to overcome this problem, there has been suggested a first
polishing apparatus in which a polishing pad mounted on a level
block is formed with a plurality of small through-holes through
which polishing slurry is supplied onto a surface of the polishing
pad from a polishing slurry source. The small through-holes are
positioned in concentration with an axis of the polishing pad 29.
Since polishing slurry is uniformly supplied between a wafer and
the polishing pad, it would be possible to keep a polishing speed
constant to thereby enhance uniformity in polishing a wafer.
There has been suggested also a second polishing apparatus in which
a polishing pad is composed of porous material in order to enhance
uniformity in polishing a wafer.
However, since a wafer having a greater diameter is compressed onto
a polishing pad at a greater pressure around a center thereof than
a periphery thereof, a polished wafer would have a cross-section
like a cross-section of a concave lens, if a wafer is polished in
accordance with the above-mentioned first or second polishing
apparatuses in which polishing slurry is uniformly supplied to a
surface of a wafer, whereas a polished wafer would have a
cross-section like a convex lens, if a wafer is polished in
accordance with the apparatus illustrated in FIG. 2.
In order to avoid this problem, Japanese Unexamined Patent
Publication No. 5-13389 has suggested a polishing apparatus which
has the same structure as that of the above-mentioned first and
second polishing apparatus, but is capable of controlling an amount
of polishing slurry at a predetermined position of a polishing pad
for the purpose of enhancing uniformity in polishing a wafer.
Specifically, the suggested polishing apparatus is formed with a
plurality of through-holes through which polishing slurry is
supplied onto a surface of a polishing pad, in such a manner that
the number of through-holes per a unit area in a region closer to a
center of a polishing pad is designed to be greater than the number
of through-holes per a unit area in a region closer to a periphery
of a polishing pad, or that a through-hole located closer to a
center of a polishing pad is designed to have a greater diameter
than a diameter of a through-hole located closer to a periphery of
a polishing pad.
A diameter of a wafer necessary to be polished is increasing. For
instance, a diameter of a wafer to be polished years ago was 6
inches (about 15 cm), but a diameter of a wafer to be polished
presently is in the range of 8 to 10 inches (about 20 to about 25
cm). Such a wafer having a great diameter could not be polished by
means of such an apparatus as illustrated in FIG. 2, because the
level block 23 has to have too much area, which results in too high
load to the apparatus.
Hence, there has been suggested such a polishing apparatus as
illustrated in FIG. 3A, in order to avoid the above-mentioned
problem. The illustrated apparatus is comprised of a rotatable
carrier 2 supporting a wafer 1 at a bottom thereof, a level block
3, a polishing pad 4 mounted on the level block 3 and positioned in
facing relation to the carrier 2, and a motor 5 for rotating the
level block 3 around a rotation axis. The polishing pad 4 is formed
with a plurality of through-holes equally spaced from one
another.
The wafer 2 is made to rotate, and then, is compressed onto the
rotating polishing pad 4. While the wafer 1 is being polished.
While the wafer 2 is being polished, slurry 6 is supplied onto a
surface of the polishing pad 4 through the through-holes.
In order to enhance uniformity in polishing the wafer 1, the level
block 3 is rotated by means of the motor 5 in such a manner that
the rotation axis of the level block 3 moves along an arcuate path.
That is, the level block 3 makes so-called orbital revolution.
FIG. 4 shows a positional relation in orbital revolution between
the wafer 1 rotating around a rotation axis A and the polishing pad
4 rotating around a rotation axis B. As illustrated in FIG. 4, if
viewed from the rotation axis A, the rotation axis B rotates around
the rotation axis A.
As mentioned earlier, if a wafer is polished with polishing slurry
being supplied onto a surface of a polishing pad through
through-holes formed with the polishing pad, there is caused a
problem that a wafer is polished to a greater degree in a central
region than in a peripheral region, resulting in that a wafer is
concave in a central region thereof. If a wafer is non-uniformly
polished as mentioned above, an electrically conductive film such
as the electrically conductive film 104 illustrated in FIG. 1D
partially remains non-removed on an insulating film such as the
insulating film 102, resulting in current leakage between
wirings.
In order to avoid such a problem, it is necessary to sufficiently
polish a wafer. However, this may result in that a wiring to be
formed on an insulating film has different heights above a central
region and a peripheral region of a wafer. Accordingly, a wiring
resistance above a central region of a wafer becomes different from
a wiring resistance above a peripheral region of a wafer with the
result of deterioration in electro-migration (EM).
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus
for polishing a wafer, which apparatus is capable of enhancing
uniformity in polishing. It is also an object of the present
invention to provide a method of doing the same.
The inventors had conducted a lot of experiments in order to
accomplish the above-mentioned object, and had found out that if a
polishing pad is designed to include a region where there are
formed no through-holes through which polishing slurry is supplied
to a surface of the polishing pad, it would be possible to enhance
uniformity in polishing a wafer.
Specifically, in one aspect of the invention, there is provided an
apparatus for polishing a substrate, including (a) a polishing pad
formed with a plurality of through-holes through which polishing
material is supplied to a surface of the polishing pad, (b) a level
block on which the polishing pad is mounted, and (c) a rotatable
carrier for supporting a substrate thereon, the carrier being
positioned in facing relation with the level block, the level block
being rotatable around a rotation axis thereof with the rotation
axis being moved along an arcuate path, and causing the polishing
pad to make contact with the substrate for polishing the substrate,
the polishing pad having a first ring-shaped region concentric
thereto where no through-holes are formed.
It is preferable that the first ring-shaped region has a width
equal to or greater than 10%, more preferably 20%, of a radius of
the polishing pad.
It is preferable that the through-holes are positioned in alignment
with a peripheral region of the substrate when an axis of the level
block is in alignment with an axis of the carrier.
It is preferable that the through-holes are positioned in a second
ring-shaped region having an outer periphery common to an outer
periphery of the polishing pad and having a width equal to 5% or
smaller of a radius of the polishing pad.
It is preferable that the polishing pad includes a circular region
concentric to the polishing pad and located inside the first
ring-shaped region, and a third ring-shaped region located outside
the first ring-shaped region, the circular region and the third
ring-shaped region including the through-holes therein. In this
arrangement, it is preferable that the third ring-shaped region has
an outer periphery common to an outer periphery of the polishing
pad. It is also preferable that the through-holes formed in the
third ring-shaped region are positioned in alignment with a
peripheral region of the substrate when an axis of the level block
is in alignment with an axis of the carrier.
It is preferable that a total area of the through-holes varies in a
radius-wise direction of the, polishing pad. For instance, the
number of the through-holes per a unit area may be designed to
decrease in a direction from an outer periphery to a center of the
polishing pad. As an alternative, diameters of the through-holes
may be designed to decrease in a direction from an outer periphery
to a center of the polishing pad.
There is further provided an apparatus for polishing a substrate,
including (a) a polishing pad formed with a plurality of
through-holes through which polishing material is supplied to a
surface of the polishing pad, (b) a level block on which the
polishing pad is mounted, and (c) a rotatable carrier for
supporting a substrate thereon, the carrier being positioned in
facing relation with the level block, the level block being
rotatable around a rotation axis thereof with the rotation axis
being moved along an arcuate path, and causing the polishing pad to
make contact with the substrate for polishing the substrate, the
polishing pad having a circular region concentric thereto where no
through-holes are formed.
It is preferable that the circular region has a radius equal to or
smaller than 95% of a radius of the polishing pad.
It is preferable that the circular region has a radius equal to or
greater than 30% of a radius of the polishing pad.
In another aspect of the present invention, there is provided a
method of carrying out chemical mechanical polishing to a
substrate, including the steps of (a) rotating a level block on
which a polishing pad is mounted, relative to a carrier on which a
substrate is mounted, around a rotation axis thereof with the
rotation axis being moved along an arcuate path, and (b) supplying
polishing material on a surface of the polishing pad while the
substrate is being polished by the polishing pad, in a region other
than a first ring-shaped region concentric to the polishing
pad.
For instance, the polishing material may be supplied on a surface
of the polishing pad through through-holes formed with the
polishing pad.
It is preferable that the polishing material is supplied on a
surface of the polishing pad in a second ring-shaped region having
an outer periphery common to an outer periphery of the polishing
pad and having a width equal to 5% or smaller of a radius of the
polishing pad.
It is preferable that the polishing pad includes a circular region
concentric to the polishing pad and located inside the first
ring-shaped region, and a third ring-shaped region located outside
the first ring-shaped region, the polishing material being supplied
into the circular region and the third ring-shaped region.
It is preferable that the polishing material is supplied onto a
surface of the polishing pad in a varying amount in a radius-wise
direction of the polishing pad. For instance, the polishing
material may be supplied in a greater amount in a region closer to
a center of the polishing pad.
There is further provided a method of carrying out chemical
mechanical polishing to a substrate, including the steps of (a)
rotating a level block on which a polishing pad is mounted,
relative to a carrier on which a substrate is mounted, around a
rotation axis thereof with the rotation axis being moved along an
arcuate path, and (b) supplying polishing material on a surface of
the polishing pad while the substrate is being polished by the
polishing pad, in a region other than a circular region concentric
to the polishing pad.
It is preferable that the circular region has a radius equal to or
smaller than 95% of a radius of the polishing pad.
It is preferable that the circular region has a radius equal to or
greater than 30% of a radius of the polishing pad.
In the apparatus in accordance with the present invention, a
polishing pad is designed to have a region in which through-holes
through which polishing material is supplied to a surface of the
polishing pad are not formed. In the method in accordance with the
present invention, polishing material is supplied to a surface of a
polishing pad in a region other than a certain region of the
polishing pad. As a result, the present invention makes it possible
to accomplish uniformity in polishing rate in a high degree. Hence,
when a buried metal layer is to be formed by chemical mechanical
polishing, a resultant semiconductor device could have superior
resistance to electro-migration (EM).
The above and other objects and advantageous features of the
present invention will be made apparent from the following
description made with reference to the accompanying drawings, in
which like reference characters designate the same or similar parts
throughout the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A to 1E are cross-sectional views of a semiconductor device,
illustrating respective steps of a method of forming a buried metal
layer by chemical mechanical polishing.
FIG. 2 illustrates a conventional apparatus for polishing a
wafer.
FIG. 3A illustrates an apparatus for polishing a wafer, to which
apparatus the present invention may be applied.
FIG. 3B is a plan view of a polishing pad employed in the apparatus
illustrated in FIG. 3A.
FIG. 3C is a plan view of another polishing pad employed in the
apparatus illustrated in FIG. 3A.
FIG. 4 illustrates a positional relation between two rotation axes
in orbital revolution.
FIG. 5 is a graph showing a relation between uniformity in a
polishing rate and a radius of a circular region in which
through-holes are closed.
FIG. 6 is a graph showing a relation between uniformity in a
polishing rate and a radius of a circular region in which
through-holes are open.
FIG. 7 is a flow chart of a method of polishing a wafer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 3A illustrates an apparatus for polishing a substrate, in
accordance with the first embodiment of the present invention.
The illustrated apparatus is comprised of a polishing pad 4 formed
with a plurality of through-holes (shown in phantom at 6A) through
which polishing slurry 6 is supplied to a surface of the polishing
pad 4, a level block 3 on which the polishing pad 4 is mounted, a
motor 5 for rotating the level block 3 around a rotation axis, and
a rotatable carrier 2 for supporting a wafer 1 at a bottom surface
thereof in facing relation with the polishing pad 4.
Though the wafer 1 is rotated around a stationary rotation axis 1A
thereof, the polishing pad 4 makes orbital revolution around the
rotation axis 1A of the wafer 1. Specifically, the level block 3
and hence the polishing pad 4 are rotated around a rotation axis 3A
thereof, and, at the same time, the rotation axis 3A is moved along
an arcuate path. That is, as illustrated in FIG. 4, if viewed from
the rotation axis 1A, the rotation axis 3A rotates around the
rotation axis 1A.
The wafer 1 is compressed onto the polishing pad 4 to thereby be
polished.
The polishing pad 4 is designed to have a first ring-shaped region
4a which is concentric to a center 4b of the polishing pad 4, as
illustrated in FIG. 3B. The through-holes through which the
polishing slurry 6 is supplied to a surface of the polishing pad 4
are formed in a region, other than the first ring-shaped region 4a,
namely, in both a circular region 4c located inside the first
ring-shaped region 4a and a ring-shaped region 4d located outside
the first ring-shaped region 4a, whereas no through-holes are
formed in the first ring-shaped region 4a.
The apparatus in accordance with the first embodiment includes the
polishing pad 4 which is designed to have the first ring-shaped
region 4a where there are formed no through-holes through which the
polishing slurry 6 is supplied to a surface of the polishing pad 4.
The wafer 1 is certainly polished in the first ring-shaped region
4a, resulting in a polishing condition where high uniformity in a
polishing rate is established.
It is preferable that the first ring-shaped region 4a has a width
equal to or greater than 10% of a radius of the polishing pad 4 for
accomplishing sufficient uniformity in a polishing rate. It is more
preferable that the first ring-shaped region 4a has a width equal
to or greater than 20% of a radius of the polishing pad 4.
It is also preferable that the polishing pad 4 is formed at a
peripheral region thereof with the through-holes. It is more
preferable that the through-holes are formed in the polishing pad 4
in alignment with a peripheral region of the wafer 1, when the axis
3A of the polishing pad 4 is in alignment with the axis 1A of the
wafer 1.
The polishing pad 4 may be designed to be formed with the
through-holes in a central region thereof, or may be designed to be
formed with no through-holes in a central region thereof. If no
through-holes are formed in a central region of the polishing pad
4, it is preferable that no through-holes are formed in a circular
region outwardly radially extending from a center of the polishing
pad 4 and having a radius equal to or greater than 30% of a radius
of the polishing pad 4.
When hard material is to be polished, it is preferable that the
through-holes are formed in a central region of the polishing pad
4, which ensures higher uniformity in a polishing rate.
In later mentioned examples, there was conducted an experiment in
which the through-holes are closed. However, in practical use, the
through-holes are formed in a polishing pad in predetermined
positions.
It is not always necessary to uniformly position the through-holes
in a surface of the polishing pad 4. A total area of the
through-holes may be designed to vary in a radius-wise direction of
the polishing pad 4. For instance, the number of the through-holes
per a unit area may be designed to decrease in a direction from an
outer periphery to a center of the polishing pad 4. As an
alternative, the through-holes may be designed to have a decreasing
diameter in a direction from an outer periphery to a center of the
polishing pad 4.
Hereinbelow are explained the experiments in which a wafer was
polished by means of the apparatus in accordance with the
above-mentioned embodiment.
EXAMPLE 1
As a wafer to be polished, there was used a wafer which had a
diameter of 8 inches (about 20 cm) and on which metal films
composed of Cu. Ta, and TiN were formed. The wafer was polished by
means of the apparatus illustrated in FIG. 3A. A polishing pad was
formed uniformly with the through-holes, and had a diameter of 10
inches (about 25 cm).
The wafer was polished with the through-holes located closer to a
center of the polishing pad, being closed one by one.
FIG. 5 shows uniformity in a polishing rate in this experiment. The
uniformity was estimated with 3.sigma. (%). The polishing
conditions were as follows.
Pressure: 3 psi
r.p.m.: 260/16
Polishing slurry supply: 100 cc/minute
The polishing slurry having been employed in this experiment was
commercially available one.
As is obvious in view of FIG. 5, the uniformity represented by
3.sigma. is equal to or smaller than 15%, if the polishing pad had
a circular region in which no though-holes are formed and which is
concentric to a center of the polishing pad and has a diameter in
the range of 1.5 inches to 4.7 inches. In particular, there is
obtained high uniformity equal to or smaller than 10%, if the wafer
had a diameter in the range of 2 inches to 4.5 inches.
Thus, it is understood from these results that high uniformity in a
polishing rate can be obtained, if a region 4e where no
through-holes are formed is formed as a circular region concentric
to the polishing pad and having a radius equal to or smaller than
95% of a radius of the polishing pad, as illustrated in FIG.
3C.
In addition, it is also understood that it is preferable that the
region 4e has a radius equal to or greater than 30% of a radius of
the polishing pad, as illustrated in FIG. 3C.
In brief, the region 4e where no through-holes are formed
preferably has a radius equal to or smaller than 0.95R, but equal
to or greater than 0.3R where R indicates a radius of the polishing
pad 4.
In particular, high uniformity in a polishing rate can be obtained
in a 8-inch wafer having been employed in the experiment, if no
through-holes are formed in the polishing pad within a circular
region concentric to a center of the polishing pad and having a
radius of 4 inches, which is equal to a radius of the 8-inch wafer,
when a rotation axis of the polishing pad is in alignment with a
rotation axis of the wafer.
Then, rates of polishing Ta and TiN both of which are generally
used as material of which a barrier film is composed were also
estimated. In the experiment for estimating the polishing rates,
the through-holes of the polishing pad were all closed in a
circular region concentric to a center of the polishing pad and
having a radius of 4 inches, and then, the through-hole located
closer to a center of the polishing pad was made open one by one.
Uniformity in a polishing rate, represented by 3.sigma., was
estimated in the same manner as the above-mentioned estimation.
FIG. 6 shows the results of the experiment. As is understood in
view of FIG. 6, uniformity of 15% or smaller can be obtained, even
if the through-holes are made open in a circular region concentric
to the polishing pad and having a radius of 3.5 inches. That is, if
the polishing pad is designed to have a region where no
through-holes are formed, which region has a width of 0.5 inches or
greater, sufficient uniformity in a polishing rate can be obtained.
Herein, 0.5 inches correspond to 10% of a radius of the polishing
pad.
There is a slight dispersion in uniformity in a polishing rate in
dependence on material of which the polishing pad is composed. For
instance, when a film composed of Ta harder than TiN is to be
polished, it is optimal that the through-holes are formed in a
circular region concentric to a center of the polishing pad and
having a radius in the range of 1.0 to 1.5 inches.
EXAMPLE 2
A semiconductor device was fabricated in accordance with the steps
illustrated in FIGS. 1A to 1E.
First, as illustrated in FIG. 1A, a semiconductor substrate 101
including active devices fabricated thereon is covered entirely
with an insulating film 102.
Then, a resist film 105 having a certain pattern is formed on the
insulating film 102, and subsequently, the insulating film 102 is
etched with the patterned resist film 105 being used as a mask, to
thereby form a contact hole 106 through the insulating film 102, as
illustrated in FIG. 1B.
After removal of the resist film 105, as illustrated in FIG. 1C, a
barrier film 103 composed of metal such as Ti or Ta is deposited
over the insulating film 102 so that the contact hole 106 is
covered at a sidewall and a bottom thereof with the barrier film
103.
Then, as illustrated in FIG. 1D, an electrically conductive layer
104 composed of copper is deposited over the barrier film 103 to
thereby fill the contact hole 106 with the electrically conductive
layer 104.
Then, the electrically conductive film 104 is planarized by means
of a chemical mechanical polishing apparatus 107, as illustrated in
FIG. 1E. Thus, a buried metal layer 108 is formed.
In Example 2, the polishing apparatus illustrated in FIG. 3A was
used as the chemical mechanical polishing apparatus 107. A wafer to
which the steps having been explained with reference to FIGS. 1A to
1D had been carried out was polished by means of the polishing
apparatus in the following conditions.
Polishing pressure: 3 psi
r.p.m.: 260/16
Polishing slurry supply: 100 cc/minute
The polishing slurry having been employed in this experiment was
commercially available. The polishing pad having been employed in
this experiment was designed to have a circular region concentric
thereto and having a radius of 4 inches.
The thus fabricated semiconductor device was estimated with respect
to resistance to electro-migration (EM). There was obtained quite
high EM-resistance.
FIG. 7 is a flow chart of a method in accordance with the present
invention.
Hereinbelow is explained the method in the assumption that the
method is carried out through the use of the polishing apparatus
illustrated in FIG. 3A.
First, in step S1, the level block 3 and hence the polishing pad 4
are made to carry out orbital revolution relative to the wafer 1
supported at a bottom of the carrier 2. Specifically, the polishing
pad 4 is rotated around the rotation axis 3A, and at the same time,
the rotation axis 3A is rotated around the rotation axis 1A of the
wafer 1 in such a manner as illustrated in FIG. 4.
Then, in step S2, the polishing slurry 6 is supplied onto a surface
of the polishing pad 4 while the wafer 1 is being polished by the
polishing pad 4, only in a region other than the ring-shaped region
4a concentric to the polishing pad 4.
Thus, the wafer 1 is polished with uniformity in a polishing rate,
in step 3.
The above-mentioned method provides the same advantages as those
obtained by the polishing apparatus in accordance with the
above-mentioned embodiment.
In the above-mentioned method, the polishing pad 4 may be designed
to be formed with a circular region where no through-holes are
formed, such as the circular region 4e illustrated in FIG. 3C, in
place of the ring-shaped region 4a.
While the present invention has been described in connection with
certain preferred embodiments, it is to be understood that the
subject matter encompassed by way of the present invention is not
to be limited to those specific embodiments. On the contrary, it is
intended for the subject matter of the invention to include all
alternatives, modifications and equivalents as can be included
within the spirit and scope of the following claims.
The entire disclosure of Japanese Patent Application No. 10-45372
filed on Feb. 26, 1998 including specification, claims, drawings
and summary is incorporated herein by reference in its
entirety.
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